Following is a list of Web Service client, server, and hybrid applications we are aware of that are supposed to handle the CSW 2.0.2 protocol. Check out OGC's registry of products for more CSW implementations.

USGIN CatalogConnector test client http://catalog.usgin.org/catalogConnector/ (version 0.5)

This promising, stand-alone, Java-based, CSW web client is currently being developed by SDI Catalonia (IDEC) and USGIN at http://sourceforge.net/projects/catalogconnecto/